The present invention generally pertains to injection molding a hollow product, and, in different aspects, is directed to (a) adjusting the dimensions of a hollow injection molded product, (b) injection molding a hollow product having a rim at an opening of the product, (c) bleeding air from a mold cavity during injection of the molding material, and (d) the characteristics of a region in which a contact surface of a stripper ring contacts a portion of a protractible and retractable core part.
It is known to control the dimensions of the sidewall of an injection molded hollow product during an initial injection of molding material by stabilizing a protractible and retractable core part within the mold cavity that shapes the hollow product. The mold cavity is positioned between a cavity section and a core section of the mold when the cavity section is combined with the core section. Stabilization of the core part is achieved by protracting the core part so that it abuts against a portion of the cavity section. This stabilization technique is described in many prior patents, including U.S. Pat. Nos. 3,737,272 to Bruno Segmuller, 4,422,995 and 5,174,941 to Jens Ole Sorensen, who is one of the inventors of the subject matter of the present invention. It is also described in Australian Patent Specification No. 17,577/70 filed by Louis Ryles.